Multiple cell electron orbiting getter vacuum pump



May 5, 1970 R. M. PHILLIPS 3,510,711

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38 |v/V/////A \F-sa s 1 I l I3 I TO SYSJTEM TO BE EVACUATED ROBERT fwfi fi s" United States Patent US. Cl. 313-7 8 Claims ABSTRACT OF THE DISCLOSURE An electron orbiting type getter vacuum pump is disclosed. The pump includes an envelope structure containing anode and cathode pumping elements. The cathode structure includes a cathode electrode partitioned into a multitude of individual elongated cathode cells with each cell containing a centrally disposed elongated anode electrode. The space within each of the cathode cells, which surrounds the anode electrode, defines an ionization region for ionizing gas particles within the pump envelope. Electrons within the cathode cells are caused to enter into relatively stable spiral orbits about the individual centrally disposed anode electrodes resulting in a spiraling cloud of orbiting electrons which collide with gas particles within the pump, thereby ionizing same. Positively ionized gas particles are driven into the cathode structure to be gettered by the reactive getter material of the cathode cell structure or to be buried in the cathode cell structure and covered over by getter material evaporated from the centrally disposed anode electrode structure. Getter material is evaporated from the anode due to electron bombardment of the anode structure by a certain fraction of the orbiting electrons which eventually are collected on the anode structure.

In a preferred embodiment, the cathode cell structure is formed by an array of parallel directed rods which define a gas permeable cathode structure permitting positive ion coupling from one cathode cell into an adjacent cathode cell for sustaining the electric discharges within each of the cathode cells. In one embodiment, certain of the cathode cell defining rods are made of materials having high electron secondary emission ratios to facilitate sustaining the electrical discharges at low pressures within the pump. In another embodiment, certain of the cathode partitioning rods comprise thermionic cathode emitters for emitting electrons into adjoining cathode cells to sustain the electric discharges therein to low pressures. In another embodiment, certain of the cathode partitioning rods are provided with sharp points or edges to provide high field electron emission into adjoining cathode cells. In another embodiment, a radioactive substance is centrally disposed of the array of cathode cells to facilitate the generation of electrons within the cathode cells. In another embodiment, an axially directed magnetic field is produced in the array of cathode cells for increasing the path length of the orbiting electrons to facilitate ionization of the gases within the pump.

DESCRIPTION OF THE PRIOR ART Heretofore, electron orbiting getter vacuum pumps have been disclosed. It has also been proposed that such pumps should include plural parallel cathode cells for increasing the pumping speed of the pump. It has also been proposed that the cathode electrode structure defining the walls of the cathode cell should be formed of a helical wire such that each cathode cell is permeable to ions which would permit ions generated Within one of the cells to pass through and be coupled into the adjoining cathode cell. Such a pump structure is disclosed in US. Pat. No. 3,244,969 issued Apr. 5, 1966. However, in the aforementioned prior art pump it has not been proposed that the cathode electrode structure should be partitioned in such a manner that the partitioning structure forms a common wall between adjacent cathode cells such that at least one of the cathode cells is surrounded by adjoining cells.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved electron orbiting getter vacuum pump.

One feature of the present invention is the provision in a multiple cell electron orbiting getter vacuum pump of means for partitioning the cathode electrode structure into an array of parallel cathode cells with at least one of the cathode cells being surrounded by adjoining cathode cells with each of the cathode cells including a centrally disposed anode electrode structure about which the electrons orbit in extended spiral paths.

Another feature of the present invention is the same as the preceding feature wherein the cathode partitioning structure is common to and is shared by the adjoining surrounding cathode cells, whereby the cathode electrode structure is simplified for multiple cell pumps.

Another feature of the present invention is the same as any one or more of the preceding features wherein the cathode cell partitioning structure includes an array of cathode rods parallel directed of the array of anode elec trodes with the cathode partitioning rods disposed surrounding each one of the elongated anode electrodes, whereby a relatively simple and highly gas permeable multiple cell cathode electrode structure is formed.

Another feature of the present invention is the same as any one or more of the preceding features wherein the cathode partitioning structure includes cathode partitioning rods disposed essentially only at the common corners of adjacent cathode cells.

Another feature of the present invention is the same as any one or more of the preceding features wherein certain of the cathode partitioning rods are made of a secondary electron emissive material selected from the class consisting of silver-magnesium, beryllium-copper, aluminum, and molybdenum, whereby the electron current within the cathode cells is augmented due to the secondary emissive characteristics of the cathode partitioning rods.

Another feature of the present invention is the same as any one or more of the preceding features wherein certain of the cathode partitioning rods include relatively sharp portions to form high field electron emitters for augmenting the electron current within the various cathode cells.

Another fcature of the present invention is the same as any one or more of the preceding features including the provision of an array of elongated thermionic electron emitters disposed parallel to the cathode partitioning rods and disposed essentially at the intersecting corners of adjoining cathode cells for augmenting the electron current within the cathode cells of the pump structure.

Another feature of the present invention is the same as any one or more of the preceding features including the provision of a radioactive substance centrally disposed of the array of cathode cells for irradiating the electrode structures and producing photo emission of electrons to augment the electron current within the pump structure.

Another feature of the present invention is the same as any one or more of the preceding features including the provision of a magnet structure for producing an 3 iaxially directed magnetic field within the array of cathode cells to increase the path length of the orbiting electrons and, thus, the ionization of gas within the pump.

Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic longitudinal sectional view, partly broken away of a multiple cell electron orbiting getter vacuum pump incorporating features of the present invention,

FIG. 2 is a sectional view of a portion of FIG. 1 taken along line 22 in the direction of the arrows,

FIG. 3 is a view similar to that of FIG. 2 depicting an alternative pumping electrode structure to that of FIG. 2,

FIG. 4 is a view similar to that of FIGS. 2 and 3 depicting an alternative pumping electrode structure to those depicted in FIGS. 2 and 3,

FIG. 5 is an enlarged sectional view of a portion of the structure of FIG. 2 delineated by line 55,

FIG. 6 is an enlarged view similar to that of FIG. 5 depicting an alternative pumping electrode structure of the present invention,

FIG. 7 is a schematic exploded perspective view of the pumping electrode structure of FIG. 6,

FIG. 8 is a view similar to that of FIG. 6 depicting an alternative pumping electrode structure of the present invention,

FIG. 9 is an enlarged view of a portion of an electrode structure similar to that shown in FIG. 6 depicting an alternative embodiment of the present invention,

FIGS. 10-12 are transverse sectional views of alternative cathode rod portions of the structure of FIG. 9 delineated by line 1010,

FIG. 13 is a view similar to that of FIG. 9 depicting an alternative electrode structure of the present invention, and

FIG. 14 is a view similar to that of FIG. 1 depicting an alternative pump embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 there is shown :a multiple cell electron orbiting getter vacuum pump 1 of the present invention. The pump 1 includes a tubular envelope structure 2 as of nonmagnetic stainless steel which may be of circular or rectangular cross section. The upper end of the envelope 2 is closed olf by a feedthrough insulator structure 3 which is hermetically sealed over the end of the envelope 2. A flange 4 is provided at the other end of the envelope 2 for mounting to a similarly flanged port on :a system to be evacuated, not shown. A pumping electrode structure 5 is disposed within the envelope 2 and is aflixed to the inside Walls of the envelope 2 by means of suitable brackets 6 as of stainless steel.

The pumping electrode structure 5, more clearly seen in FIG. 2, includes a hollow rectangular sheet metal electrode structure 7 operated at ground potential. The rectangular structure 7 is open on the ends and is partitioned into a multitude of approximately square cross section cells 8 by means of an egg-crate shaped sheet metal partitioning structure 9 made of a suitable getter material as a titanium. An array of elongated anode wires or rods 11 are coaxially disposed within each of the cathode cells 8. The cathode cells 8 extend the full axial length of the pumping electrode structure 5 to define an array of electron orbiting type pumping cells.

A pair of screen electrodes 12 and 13 (see FIG. 1) close off the opposite ends of the cathode cells 8. The screens 12 and 13 are electrically connected to the cathode 7 and operate at cathode potential for reflecting the orbiting electrons to and fro along the length of the cathode cells 8. The anode rods 11 are supported from the cathode screen structures 12 and 13 by a means of cylindrical insulator bodies 14, as of ceramic, more clearly seen in FIG. 7. The anode rods 7 are connected together by means of leads 15 and are energized with a suitable anode potential as of +3 kv. to 10 kv. from a suitable potential source 16 by means of lead 17.

Referring now to FIG. 5 the mode of operation of the pumping electrode structure is more clearly depicted. In cell (a) an orbiting electron 18 spirals about the centrally disposed anode rod 11 in a spiral path. The spiraling electron 18 collides with a neutral gas molecule as depicted in cell (b) to produce a positive ion 19 and an additional electron 21. As shown in cell (c), the original electron 18 and the electron 21 produced by the ionizing collision continue the spiral orbits about the anode electrode 11. If the positively ionized gas particle 19 is inert, as of argon, it is accelerated towards and driven into the cathode partition 9 where it is buried and subsequently covered over by condensed getter material. If the ion 19 is of an active material such as nitrogen it is gettered by the getter material of the partition 9 or by condensed getter material deposited upon the surface of the partition 9. In this manner, gas particles within the pumping element 5 are pumped.

If the cathode partitioning structure 9 is perforated such that it is permeable in certain locations to positive ions as shown in cell (d), the ion 19 may pass through the partition 9 into an adjoining cell as shown in cell (c). In such a case, the positive ion 19 will be gettered or otherwise removed from the vacuum within the adjoining cell (e) in the manner as previously described with regard to the operation in cell (c). When the partition 9 is permeable to the positive ions it serves to provide an ion coupling fro-m one cell into an adjacent cell to facilitate maintenance of the electric discharges within the cells 8 of the pumping structure 5. This occurs because the positive ion 19 may collide with a gas molecule or particle within the adjoining cell to produce ionizing collisions, thereby generating an electron which can enter into and sustain the electric discharge within the adjoining cell or it may produce a secondary electron upon collision with the cathode partitioning structure, t-hereby releasing an electron or electrons which may enter into orbits about the anode electrode 11.

Referring now to FIG. 3, there is shown an alternative pumping electrode structure 5' wherein the cathode partitioning structure 9 is arranged to produce triangular cross section cathode cells 8. The triangular cross sectional cathode cells 8 of FIG. 3 operate in substantially the same manner as previously described with regard to the square cross sectional cells of FIGS. 2 and 5.

Referring now to FIG. 4, there is shown an alternative pumping electrode structure 5" wherein the cathode partitioning structure 9 defines an array of hexagonal cross sectional cathode cells 8. The hexagonal cells 8 of FIG. 4 operate in substantially the same manner as previously described for the square cross sectional cells 8 of FIGS. 2 and 5.

In one embodiment of the present invention, the anode rods 11 are made of a getter material such as titanium. A certain fraction of the orbiting electrons eventually bombard the anode rods 11 to produce heating thereof. The rods are heated to a sulficient temperature by the electron bombardment to cause evaporation of the getter material. The getter material is collected on the interior surfaces of the cathode partitions 9 for covering over the buried inert gas ions as, for example, argon and the condensed layer also provides an active layer for gettering active neutral gases coming in contact therewith.

Referring now to FIG. 6 there is shown an alternative pumping electrode structure 5 similar to that shown in FIGS. 2 and 5 with the exception that the cathode partitioning structure 9 is formed by a plurality of cathode rods 25 made of a suitable getter material such as, for

example, titanium. The rods 25 make electrical contact with the screen structures 12 and 13 at the ends of the pumping electrode structure 5 and provide gas permeable partitioning walls 9, as previously described with regard to FIG. 5. The cathode partitioning rods 25 provide a convenient way to form the permeable partitioning walls 9.

Referring now to FIG. 7, there is shown an exploded perspective view of the pumping electrode structure 5 employing the cathode partitioning rods 25, as previously described with regard to FIG. 6. The cathode partitioning rods 25 are inserted axially into the rectangular cathode electrode structure 7 to partition the rectangular structure 7 into the individual elongated cathode cells 8. Likewise, the anode electrode structures 11 are axially inserted through the screens 12 and 13 into the partitioned cathode electrode structure. The ceramic insulative sleeves 14, which are carried at the ends of the anode rods 11, serve to insulate the anode electrodes 11 from the grounded screen electrodes 12 and 13.

Referring now to FIG. 8, there is shown a pumping electrode structure 5 similar to that depicted in FIG. 6 with the exception that the cathode partitioning rods 25 are provided essentially only at the corners of the adjoining cathode cells 8. The imaginary boundary walls of the partitioned anode cells 8 are indicated by the dotted lines. By providing the partitioning cathode rods 25 essentially only at the corners of the adjoining anode cells 8, a relatively open cathode cell structure is produced which facilitates establishment of positive ion orbits about the corner cathode rods 25. These orbits substantially extend the path length of the positive ions to facilitate additional ionization of gas particles within the pumping electrode structure 5 by collision between the positive ions and gas particles. These extended ion orbits also enhance the ion coupling between the various pumping cells 8 such that the electrical discharges in the pumping structure 5 are sustained to lower pressures. In this version of the pump, the positive ions which orbit around the corner rods 25 are accelerated toward the nearest end screen 12 or 13. The orbiting ion will either strike the screen 12 or 13 or pass through the screen striking the end wall of the pump. In one embodiment, pumping is facilitated by replacing the screens 12 and 13 by plates of getter material as of titanium or by placing titanium plates between the screens 12 and 13 and the end walls of the pump. The mode of operation is depicted in cells (a), (b) and (0).

Referring now to FIG. 9, there is shown an alternative embodiment of the present invention wherein certain of the cathode partitioning rods 25' are made of a material having a relatively high secondary electron emission ratio. Such materials include materials selected of the class consisting of silver-magnesium, beryllium-copper, aluminum, and molybdenum. The secondary emitter rods 25', upon being bombarded by the positive ions, produce a relatively high yield of secondary electrons which enters into the orbiting electron cloud surrounding the anode electrodes 11 to facilitate ionization of gas particles within the pump and, thus, enhancing the pump ing speed of the pump. The sequence of operation is depicted in cells ('a)(d).

As an alternative to the secondary emitting rods 25 these rods may be shaped to have sharp edges or points as shown in FIGS. -12 to provide high field emission of electrons from the rods 25" into the cathode cells 8 to facilitate starting of the electric discharge and to enhance the pumping speed of the pump by augmenting electron space charge. In FIG. 10, the high field emission rod 25" has a square cross section to provide sharp corners to facilitate high field emission. In FIG. 11 the high field emission rods 25" have a star-shaped cross sectional configuration to provide the high field emitting edge. In FIG. 12, the high field emission rods 25" include a multitude of outwardly directed spikes or points to facilitate high field emission therefrom.

Referring now to FIG. 13, thermionic emitter rods 31 are provided at the intersecting comers of each four adpoining cathode rod partitioned cells 8. At the intersecting comer, the cathode partitioning rods 25 are arranged in a pair of rows 32 to provide focusing cathode electrode structures such that the electrons emitted from the thermionic emitter 31 are projected into the adjoining four anode cells 8 with a substantial tangential component to facilitate launching of the electrons into spiral orbits about the anode rods 11. Although the filamentary emitter 31 can be operated at the same potential as cathode rods 25, a higher percentage of stable orbits for the emitted electrons 18 can be achieved if the potential applied to the cathode emitter 31 is a potential slightly more positive than that applied to rods 25 such that the electrons 18 emitted from the thermionic emitter 31 cannot reach the grounded cathode rods 25. The four-cell pattern employing a centrally disposed cathode emitting filament 31 may be repeated throughout the array of cathode cells of the pumping electrode structure 5. However, there need not be provided one filamentary emitter for each four cathode cells 8, as the positive ion coupling between the cells will allow spreading of the electrical discharge from one cell 8 throughout a substantial number of cells 8. In such a case, it would be sufficient to use only a single filament 31 centrally disposed of the array of cathode cells 8. The filamentary emitter 31 augments the electron space charge and facilities starting of the pump and permits the pump to operate to lower pressures.

In another embodiment of the present invention some initial ionization of gas molecules is achieved by placing a radioactive substance on the center-most rod 25 of the array of cathode partitioning rods 25. The radioactive decay gives off high energy particles which, when captured by the surrounding electrode structure, results in photoemission of high energy electrons within the pumping electrode structure 5. These electrons cause ionization of residual gas molecules within the pump electrode structure 5 to facilitate starting of the pump.

Referring now to FIG. 14, there is shown an electron orbiting pump similar to that depicted in FIG. 1 and including a magnet structure 33 for providing an axially directed magnetic field B as of between 5'0 and 200 gauss within the pumping structure 5 to enhance the pumping speed of the pump.

The magnet structure 33 includes a plurality of bar magnets 34 disposed about the circumference of a pump envelope 2 on the outside thereof. A pair of magnetic pole structures 35 and 36, as of mild steel plate, are disposed at opposite ends of the pumping electrode structure 5. The lower plate 36 is performated to permit gas passage therethrough from the system to be evacuated to the pumping electrode structure 5. The bottom plate 36 forms a portion of the pump envelope and also forms the flange 4 for connecting the pump 1 to the system to be evacuated. The upper pole structure 35 includes plate 35 carried within the envelope 2 by means of a plurality of brackets 37. A ring-shaped portion 38 of the envelope 2 is made of a magnetic material such as magnetic stainless steel and extends outwardly from the envelope 2 to abut the poles of the permanent magnets 34.

The axially directed magnetic field B provides a magnetic field component orthogonal to the radial electric field E between the anode and the cathode structures for extending the path lengths of the orbiting electrons.

Although the magnet structure 33 is depicted as a permenent magnet in the apparatus of FIG. 14, the permanent magnets 34 may be replaced by an electrical solenoid 41, as shown in FIG. 1. The electric solenoid 41 is energized from a source of direct current 42 to produce the axially directed magnetic field B in the pumping electrode structure 5.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention can be made without departing from the scope thereof it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In an electron orbiting getter vacuum pump; means forming a hollow cathode electrode structure; means forming an anode electrode structure disposed within and spaced from said cathode structure to define an ionization region therebetween in which electrons are caused to enter into spiral orbits having extended path lengths about said anode electrode structure for ionizing gaseous particles within the ionization region; said cathode electrode structure including, means for partitioning said cathode electrode structure into an array of parallel cathode cells with at least one cathode cell being surrounded by adjoining cathode cells, said anode electrode structure including an array of elongated parallel electrodes with one of said anode electrodes of said array being centrally disposed in each of said cathode cells the improvement wherein said cathode cell partitioning structure includes an array of cathode rods parallel directed of said array of anode electrodes, said cathode rods being disposed surrounding each one of said elongated anode electrodes.

2. The apparatus of claim 1 wherein each of said cathode cells has at least three sides, and said cathode partitioning rode are disposed essentially only at the common intersecting corners of said cathode cells.

3. The apparatus of claim 1 wherein at least one of said cathode partitioning rods is made of a getter material.

4. The apparatus of claim 1 wherein at least certain of said cathode partitioning rods are made of a secondary electron emissive material selected from the class consisting of silver-magnesium, beryllium-copper, aluminum, and molybdenum.

5. The apparatus of claim 1 wherein certain of said cathode partitioning rods include relatively sharp portions to form high field electron emitter portions.

6. The apparatus of claim 1 including means forming at least one thermionic electron emitter disposed parallel to said cathode partitioning rods and disposed essentially at the intersecting corner of adjoining cathode cells.

7. The apparatus of claim 1 including means forming a magnet structure for producing an axially directed magnetic field within said cathode cells.

8. The apparatus of claim 1 including a radioactive substance centrally disposed of said array of cathode cells.

References Cited UNITED STATES PATENTS 3,233,825 2/1966 Asamaki 313-7 X 3,244,969 4/1966 Herb et al. 3l3-7 X 3,339,106 8/1967 Redhead 3137 X 3,352,482 11/1967 Forrester et al. 23069 3,387,175 6/1968 Lloyd et a1 313-7 X RAYMOND F. HOSSFELD, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R. 230-69 

